Hereditary pontine and extrapontine brain malformations in Brazilian Tabapuã cattle

Abstract

A congenital neurologic disorder affected a herd of Tabapuã cattle. Of 98 newborn calves, 12 (12%) were affected; they were sired by 3 related bulls. This frequency suggested a genetic disorder caused by an autosomal recessive gene. Persisting recumbency, an altered sensorium, head tilt, nystagmus, episodic head and neck jerking, ventral strabismus, and opisthotonic posturing resulted in euthanasia by day 15. The postmortem findings were similar in 8 calves studied. The skull was smaller and flattened compared with unaffected calves. The cerebral hemispheres were slightly reduced in size with their gyral pattern simplified and showing occasional, focal macrogyria. The corpus callosum was partly aplastic. The pons held the most striking gross abnormality, namely, the absence of the pontine base and middle cerebellar peduncles while the trapezoid body in the medulla was reduced. There was severe hypoplasia of pontocerebellar fibers and a mildly reduced size of spinothalamic, corticospinal, and corticobulbar tracts. Histologically, numbers of neurons in the pontine basal, red, olivary, and cerebellar nuclei were reduced. Neurologic signs reflect these extensive pathologic changes, especially in the midbrain, brainstem, and caudal fossa. While olivopontocerebellar anomalies are known in domestic animals, selective pontine hypoplasia has not been reported. These Tabapuã calves share features of pontocerebellar hypoplasia (PCH), a human malformation, in which the pons and the cerebellum are most severely affected with impaired growth of other parts of the brain leading eventually to microcephaly. At least, 11 different forms of human PCH are related to mutations in several different genes.